Heretofore, numerous types of optical image correlators have been known whereby a live or real scene may be correlated with a reference image in such a manner that an output signal, indicative of the degree of correlation between the two, is produced. Such optical image correlators have been most generally used in guidance systems for aircraft, missiles, and the like. Applicants are particularly aware of U.S. Pat. Nos. 3,723,717; 3,751,705; 3,748,042; 3,496,290; 3,514,535; 3,564,126; and 3,609,762, all of which are assigned to Goodyear Aerospace Corporation of Akron, Ohio, the assignee of the instant invention. All of the foregoing prior art references teach an optical image correlator wherein a photocathode converts light impinging thereupon into a corresponding electron stream which is accelerated through a vacuum tube for storage on a storage grid. The electron stream is focused onto the storage grid by means of an electromagnetic coil or the like. A collecting screen is provided closely adjacent the storage grid to accommodate secondary emissions therefrom. With the reference image so stored, a live image may be converted into an electron stream and directed toward the storage grid. This electron stream is nutated by means of electromagnetic deflection so that the live image is nutated over the reference image maintained upon the storage grid. Electrons passing through the grid are sensed at an anode which produces an output current directly related to the degree of correlation existing between the live input image and the reference image maintained on the storage grid. A further detailed understanding of the prior art may be had by reference to the foregoing prior art citations.
While the prior art approach to optical image correlation has been generally satisfactory, certain problems have been existent therewith. Indeed, all problems commonly inherent with vacuum tubes have been experienced in the use of such correlators. The inaccuracies incident to the utilization of magnetic deflection coils for nutation and focusing have been difficult and expensive to circumvent or overcome. The susceptibility of such systems to damage by the jolting and jarring characteristic of their operational environment has been ever present. The prior art teachings have, by and large, utilized a totally analog technique in the correlation process and, consequently, have suffered from the inaccuracies inherent therewith. In general, the prior art has suffered from a lack of a digital solid state optical image correlating apparatus and technique.